testDms: version has no special meaning to system.

Specifically, system must not compare version to decide which is older, and
does not. So remove noise from test, and reword docstring.
erp5_dms: Only archive other versions when effective date is reached.

Also, make effective date visible and editable on relevant document views
lacking it.
Add a test.
erp5_web: Use "limit" so sort is applied before projection.

As this means sorting had no effect, drop sorting on versions: versions
are arbitrary strings which can have any evolution scheme, so do not try
to guess what is more recent than something else.
erp5_web: Take effective_date into account when looking content up.

effective_date, when defined, prevents a document from being visible even
if it is in the correct workflow state.
Note that this is orthogonal with workflow states: a document which must
not be visible should not be in a workflow state which makes it visible to
begin with. effective_date only affects website-style document listing and
lookup.